Synthesis, characterization, and application of nanoporous carbon membranes

Inorganic membranes offer significant potential advantages over polymer membranes, but only if they can be fabricated readily and reproducibly. Zeolites, sol-gels and nanoporous carbons are each being investigated for this purpose. Membrane synthesis and fabrication have proven to be critical problems with each of these materials because continuous defect-free films are difficult to achieve. This work has sought to avoid this problem by forming nanoporous carbon layers on an underlying support such as porous sintered metal, to provide the necessary mechanical strength. These materials are more robust, and display good selectivities, but ease of fabrication and reproducibility remained a challenge.; The deposition of the polymeric carbon precursor and pyrolysis are two key steps in fabrication that must be precisely controlled in order to produce thin continuous films consistently. This thesis describes a new technique using ultrasonic deposition for applying thin, uniform layers of polyfurfuryl alcohol to porous stainless steel tubes. After pyrolysis, films deposited in this way resulted in the formation of the first tubular, crack-free nanoporous carbon membranes. These supported nanoporous carbon membranes show unprecedented size and shape selectivities, even among very small molecules such as oxygen and nitrogen which have similar dimensions. Microscopy and porosimetry were used extensively to characterize carbon film properties and pore size distribution. Mean pore size was centered round an average of 0.45 to 0.50 nm, which is the size necessary to separate gases such as oxygen and nitrogen. Additives such as titanium dioxide, small pore high silica zeolites, and polyethylene glycol were added to the polyfurfuryl alcohol precursor for modification of the carbon film to increase selectivity and flux. Alternative high energy heating sources such as a continuous carbon dioxide laser were also investigated for reducing the time necessary to manufacture these thin supported carbon films.; Continuous separation of oxygen from air, para-xylene from xylene isomers, nitrogen and carbon dioxide removal from natural gas, and hydrogen from hydrogen chloride have all been demonstrated.